CuFeS2 is an altermagnetic semiconductor that is lattice-matched with silicon and has a high N\'eel temperature. It is nonpolar and magnetically compensated in its structural ground state. However, the crystal belongs to a magnetic symmetry class allowing simultaneous piezoelectricity and -magnetism, indicating that distortion by shear strain may enable functional properties not observed in its tetragonal ground state. This first-principles study explores how biaxial and shear strain affect the crystal structure and functional properties. Biaxial strain lowers crystal symmetry when applied to two of the three crystallographic {001} planes considered, enhancing the altermagnetic lifting of the Kramers degeneracy. Shear strain has a compressive effect on the crystal, enhancing the effects on the electronic structure seen under biaxial compressive strain. Applying it to any one of the three {001} planes induces a polar phase with an out-of-plane electric polarization, perpendicular to the strained plane. Moreover, applying shear strain to two out of the three {001} planes induces a net magnetization simultaneously with electric polarization, producing a multiferroic response.
@article{arxiv.2503.21637,
title = {Shear Strain-Induced Multiferroic Response in the Altermagnetic Semiconductor CuFeS$_2$},
author = {Roman Malyshev and Bjørnulf Brekke and Ingeborg-Helene Svenum and Sverre M. Selbach and Christoph Brüne and Arne Brataas and Thomas Tybell},
journal= {arXiv preprint arXiv:2503.21637},
year = {2025}
}